COASTAL EROSIONAL LANDFORMS

GEOL 1053

LIST OF MAJOR COASTAL EROSIONAL LANDFORMS

(involving consolidated rocks)• Sea cliffs

• Wave-cut platform

• Sea arches

• Sea stacks

• Sea caves

• Coastal waterfalls

WAVE-CUT PLATFORMS• Erosion of a sea cliff leaves

a gently sloping rock platform that is visible at low tide. It may be partly covered by a veneer of coarse-grained sediments, even cobbles and boulders.

wave-cut notch

wave-cut platform

Wave-cut platform: Headland and beach cut on Oligocene Amuri Limestone. (south of Kaikoura, South Island, New Zealand)

Wave-cut platform

SEA ARCHES:

• Differential weathering at tide level along a narrow promontory.

• Natural bridge (sea arch) in Plio/Pleistocene limestone (North coast of Aruba).

SEA STACKS• More resistant rock remains as a promontory because of compositional or

structural differences which lead to differential weathering & collapse of arches.

• Sea stacks and sea arches in cyclically bedded Upper Cretaceous chalks (French Channel coast).

SEA STACKS (CONT.)

Sea stacks along a cliffed, rocky coastline (Victoria coast,Australia). Large waves from the Southern Ocean have erodedfractured sandstones into a series of headlands and isolatedstacks (remnants of headlands). Although clearly vulnerable towave erosion, such stacks survive for tens to hundreds of years.

SEA CAVES

• Deep erosion locally in a sea cliff

• Of weaker rocks

• At tide level

• “Blowholes” may develop where roofcollapses

COASTAL WATERFALLS

• when horizontal cliff erosional retreat is faster than stream bed erosion downward

• produces a “hanging valley”

Evolution of a drowned coastline

(ria coast):

There is a tendency for the coast to straighten - all other factors being equal (more resistant rocks will form headlands while the less resistant rocks will form embayments). Bays fill with sediments.

- erosion occurs

- sediments form

- shoals develop

- depositional landforms (beaches, spits, etc.) develop

Large erosional talus blocks of Pleistocene limestone that have tumbled down the erosional escarpment that exposes the Scotland Fm. in the background. Note the wave-cut notches at the base of the talus blocks. Such notches, cut by physical and biological processes, are excellent indicators of sea level and can be preserved in some circumstances. Human bathers. (Bathsheba, Barbados)

END OF FILE

Rocky, tectonically active, immature coastline with numerous small offshore sea stacks and islands(San Francisco-Mendocino area, California).